The present invention relates to a device transfer method and a display apparatus. More particularly, the present invention relates to a device transfer method and a display apparatus by or in which devices can be transferred accurately.
In the case of assembling an image display apparatus by arranging light-emitting devices in a matrix, it has been a general practice to form the devices directly on a substrate as in the cases of liquid crystal displays (LCD) and plasma display panels (PDP) or to arrange singular light-emitting diode (LED) packages as in the case of light-emitting diode displays (LED displays). For example, in such image display apparatuses as LCD and PDP, device separation is not possible, so that the individual devices generally are formed at intervals corresponding to the pixel pitch of the desired image display apparatus, from the beginning of the manufacturing process.
On the other hand, in the case of LED displays, LED chips are taken out after dicing, and are individually connected to external electrodes by bump connection through flip chips or wire bonding, to thereby achieve packaging. In this case, the devices are arranged at the pixel pitch of the image display apparatus before or after the packaging, and the pixel pitch is independent of the pitch of the devices at the time of forming the devices.
Since the LEDs (light-emitting diodes) as light-emitting devices are expensive, the cost of the image display apparatus using the LEDs can be lowered by producing a large number of LED chips from one sheet of wafer. Namely, when the size of the LED chips is changed from the conventional size of about 300 μm square to a size of several tens of micrometers square and the thus reduced LED chips are connected to manufacture an image display apparatus, the cost of the image display apparatus can be lowered.
Meanwhile, in relation to the manufacturing step for manufacturing a desired apparatus by rearranging onto an apparatus substrate a plurality of devices formed on a device formation substrate, there has been practiced a device arranging method in which devices are transferred onto an adhesive layer provided on a device holding substrate for temporarily holding the devices and, thereafter, the devices are transferred onto the apparatus substrate serving as the final destination of arrangement, for arranging the devices.
In transferring the devices from the device holding substrate onto the apparatus substrate, a method of dropping an adhesive onto the devices temporarily fixed on the device holding substrate and, thereafter, adhering the apparatus substrate thereto has been adopted. In this case, the device holding substrate and the apparatus substrate are adhered to each other, and then the device holding substrate and the apparatus substrate are stripped from each other; in this process, it is difficult to strip the device holding substrate and the apparatus substrate from each other, due to the strong adhesion therebetween by the adhesive. Particularly, in the case of lamination of substrates having large areas, it is highly possible that the substrates may be damaged at the time of stripping. Furthermore, since the adhesive layer is hardened (cured) in the condition where the devices are embedded in the adhesive layer, it is difficult to transfer the devices onto the apparatus substrate and thereafter again transfer devices onto the same apparatus substrate.